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    Subject[PATCH printk v4 1/6] lib/nmi_backtrace: explicitly serialize banner and regs
    Date
    Currently the nmi_backtrace is serialized against other CPUs because
    the messages are sent to the NMI buffers. Once these buffers are
    removed, only the dumped stack will be serialized against other CPUs
    (via the printk_cpu_lock).

    Also serialize the nmi_backtrace banner and regs using the
    printk_cpu_lock so that per-CPU serialization will be preserved even
    after the NMI buffers are removed.

    Signed-off-by: John Ogness <john.ogness@linutronix.de>
    Reviewed-by: Petr Mladek <pmladek@suse.com>
    ---
    lib/nmi_backtrace.c | 7 +++++++
    1 file changed, 7 insertions(+)

    diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
    index 8abe1870dba4..dae233c5f597 100644
    --- a/lib/nmi_backtrace.c
    +++ b/lib/nmi_backtrace.c
    @@ -92,17 +92,24 @@ module_param(backtrace_idle, bool, 0644);
    bool nmi_cpu_backtrace(struct pt_regs *regs)
    {
    int cpu = smp_processor_id();
    + unsigned long flags;

    if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
    if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
    pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
    cpu, (void *)instruction_pointer(regs));
    } else {
    + /*
    + * Allow nested NMI backtraces while serializing
    + * against other CPUs.
    + */
    + printk_cpu_lock_irqsave(flags);
    pr_warn("NMI backtrace for cpu %d\n", cpu);
    if (regs)
    show_regs(regs);
    else
    dump_stack();
    + printk_cpu_unlock_irqrestore(flags);
    }
    cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
    return true;
    --
    2.20.1
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